Sourav hits the nail on the head… the criticism is because CMF markets the device as customisable and, reviewers leaned into the modular narrative but, with the omission of a removal battery which felt like a big miss. It also seems that due to the accessory point, the reparability is slightly more challenging vs. a device without it.
From my POV, the phone has 2yrs of major updates & 3yrs of security updates, the devices affordability means that most users will update after this period and the battery will still be of good health, there’s probably few use cases for actually replacing the battery for the 99% of buyers. This is the old what tech consumers want vs. what is useful / wanted/used by the majority.